1. Field of the Invention
This invention is concerned with a novel class of liquid crystalline amines which exhibit low temperature liquid crystalline phases.
2. Description of the Prior Art
Liquid crystals are organic compounds which exhibit certain of the properties of conventional liquids and certain of the properties of conventional crystals. Detailed discussions of the types of liquid crystalline phases and their applicability to optical display devices may be found, for example, in A. R. Kmetz, and F. K. von Willisen, editors, "Non-Emissive Electrooptic Displays", Plenum Press, New York (1976). Desirable features of liquid crystals to be used in electro-optical display devices are stability, room temperature nematic liquid crystalline phases and a wide nematic range.
It has generally been thought that amino functionalities placed at or near the end of a potential liquid crystalline molecule do not allow for the existence of liquid crystalline properties. Three exceptions to this general rule are known.
The first exception occurs when an intramolecular hydrogen bond exists in the molecule as in Formula 1 below: ##STR1## In contrast, intermolecular hydrogen bonding (typical of terminal amino substituted compounds) has been postulated to promote a non-linear molecular array detrimental to liquid crystalline phases.
The second exception is based on electron donation by (OH) or (NH.sub.2) groups which may promote polar resonance contributors in a molecule. This increases intermolecular attractions and thus promotes a liquid crystalline phase. A molecule such as Formula 2 is capable of such resonance. ##STR2##
The third exception occurs when the amine is incorporated into a largely conjugated rodlike molecule, such as Formula 4. ##STR3## In such molecules other favorable structural factors may outweigh the possible deleterious effects of hydrogen bonding. The foregoing characterizations of the "general rule" and the exceptions thereto are based on:
P. Culling, G. W. Gray and D. Lewis, J. Chem. Soc. 2699 (1960);
D. C. Schroeder and J. P. Schroeder, J. Am. Chem. Soc. 96, 4347 (1974);
D. C. Schroeder and J. P. Schroeder, J. Org. Chem. 41, 2566 (1976);
M. J. S. Dewar and R. S. Goldberg, J. Org. Chem. 35, 2711 (1970);
"Flussige Kristalle in Tabellen", VEB Deutscher Verlag fur Grundstoffindustrie, Leipzig, 1974, pp. 88-89.
Notwithstanding the foregoing contraindications, the general objective of the present invention is to provide a low temperature liquid crystalline structure with terminal, primary or secondary amino polar electron donating groups.
A more specific object of this invention is to provide mesophasic amine terminal derivatives containing the phenylcyclohexane bicyclohexyl or biphenyl ring systems.
An additional object of this invention is to provide stable, nematic type liquid crystal compositions of increased nematic range which exhibit room temperature nematic phases. Such compositions are of use in electro-optical display devices.